Natural teeth show a quite complex gradient in translucency, beginning from translucent (enamel) to nearly opaque (dentin) from the outer to the inner area. Translucency is therefore a desired property of dental materials where esthetic matters.
Currently, in trying to achieve highly esthetic ceramic restoration, the high strength ceramic (e.g. zirconia) material is typically veneered with a low strength high translucent and typically glass-ceramic based veneering material.
In most cases, the veneering step is done by a skilled lab technician and is often time consuming and expensive. Due to the weakness of the veneering porcelain chipping is often observed in a variety of clinical cases.
Another way to produce dental restorations is using a so-called monolithic zirconia material without applying a veneering step. This possibility is typically chosen for situations where esthetics plays only a minor role (e.g. in the posterior regions of the dental situation).
Zirconia based dental restorations are typically produced via a CAD/CAM process:                A dental restoration is milled out of a pre-sintered zirconia mill blank.        Afterwards the esthetic of the dental restoration is increased by coloring the material with a suitable coloring liquid.        The dental restoration is finished by sintering and polishing.        
In the field of glass ceramics a couple of layered blocks with different degrees of translucency are meanwhile commercial available.
E.g. Vita Company offers a so-called TriLux™-block (having planar layers) as well as the so-called TrueLife™ block (having a conical core).
These blocks are designed for so-called chair-side dental restorations, that is, dental restorations which are manufactured when the patient to be treated is still in the office of the dentist.
Producing these kinds of blocks out of zirconia materials having different translucencies is, however, not possible due to different sintering temperatures needed for sintering the individual materials.
The sintering of tetragonal zirconia (e.g. 3Y-TZP: Tosoh Corp., Japan) is typically done in a range of 1350° C. to 1550° C., whereas the sintering of cubic zirconia or fully stabilized zirconia (e.g. 10Y-ZP: supplier e.g. Tosoh Corp., Japan) is typically done at a temperature above 1550° C.
During a co-firing process, a zirconia block being prepared out of these materials will typically break or show fractures.
In U.S. application 61/545,243 (3M IPC) aerogels, calcined and crystalline articles and methods of making the same are described.
US 2011/0269618 (Knapp et al.) relates to nano-crystalline dental ceramics, where the nanocrystals are formed by vaporization.
US 2012/0156472 (Brännvall et al.) relates to a dental application body comprising an oxide ceramic containing a bulk material containing an oxide ceramic and at least one coating containing yttrium oxide and/or cerium oxide stabilized zirconium oxide. It is stated that the yttrium oxide and/or cerium oxide stabilized zirconium oxide coating powder forming the basic raw material for the coating has a particle size of between 0.20 and 1.00 μm. The thickness of the coating is typically with a range of 5 to 300 μm. The dental application body is said to have improved aging capability and can be used as bone anchored implant.